1. Field of the Invention
The present invention generally relates to a pressure-sensitive electromagnetic pointer and the control method thereof, and more particularly to an electromagnetic pointer and the control method thereof which use the writing force applied upon to suddenly alter the emitting frequency.
2. Description of the Related Art
The operation principle of electromagnetic type input technology is performed by a circuit board with a plurality of antennas or sensor coils arranged along axial directions and an electromagnetic pen which can emit electromagnetic signals. The sensing plane of an electromagnetic input apparatus includes a plurality of antennas or sensor coils. The antennas or sensor coils are arranged under a work surface or a display panel of the electromagnetic input apparatus. The coordinates of the electromagnetic pen are obtained through the transmitting and receiving of electromagnetic waves between the circuit of the electromagnetic pen and the antennas or the sensor coils.
Input apparatuses which use the electromagnetic type input technology comprise smart mobile devices (Smart Phone), digitizers or tablets or e-books/green books and are used with electromagnetic pens or styluses.
The circuit of the electromagnetic pen usually comprises an inductor, a capacitor and relative components enclosed in a case. The inductor constituted by a ferrite core winded with a metal coil and the capacitor constitute the circuit to transmit and receive electromagnetic signals with the antennas or sensor coils. The frequency of the circuit is determined according to the capacitance and the inductance connected in parallel. When a user utilizes the electromagnetic pen to perform writing function on the input apparatus, the tip of the electromagnetic pen being pressed would induce the continuous changes of the inductance or capacitance as well as the frequency of the circuit. The input apparatus detects and calculates the frequency of the electromagnetic signals received to obtain pressure levels of the electromagnetic pen via an internal circuit.
For example, in U.S. Pat. No. 5,206,785, the main design principle involves continuous variation of capacitance induced by pressing the pen tip. While in U.S. Pat. No. 5,565,632, the disclosure involves continuous variation of inductance caused by pressing the pen tip. The designer of the electromagnetic pen can choose either the inductor or capacitor to be variable or adjustable according to the requirement and determine the variation ranges of the capacitance or inductance.
Both the two principles set forth have a disadvantage. Since both principles involve continuous variations of inductance or capacitance, the frequency variations caused by the displacement of the pen core structure may not be detected or the frequency variations are very tiny such that the input apparatus is unable to detect the frequency variations when the pen tip of the electromagnetic pen is pressed by a relatively small force. These design principles are not able to allow a user to start writing just after slightly touching the pen tip.
In US Pub. 20110175845, the operation principle involves a structure of activating a micro switch via a pen tip. The electromagnetic pen lacks a structure of variable inductor or capacitor varying according to the displacement of the pen tip. Thus the frequency of the oscillation circuit of the electromagnetic pen is unable to vary along with the displacement of the pen tip. The electromagnetic pen with such design structure does not have a pressure-sensitive level function of pen tip.
In view of the above shortcomings of the previous designs, the invention provides a new electromagnetic pointer and the control method thereof. When a user utilizes the electromagnetic pointer with an input apparatus, the tip of the electromagnetic pointer with a micro force applied upon suddenly alters capacitance connected in parallel with the oscillation circuit of the electromagnetic pointer so as to discontinuously change the emitting frequency of the electromagnetic pointer at the beginning of the pressing of the tip through the pressure-sensitive level function of the tip of the electromagnetic pointer.